1. Technical Field
This invention relates to a method of discriminating the present position region of a machine.
2. Description of the Related Art
Conventionally a numerically controlled (hereafter referred to as "NC") machine tool has a dog provided on a movable portion of the machine tool and a limit switch provided at a prescribed position on a stationary portion of the machine tool. When the dog trips the limit switch, a signal is generated that the movable portion of the machine has reached the prescribed position, whereupon a predetermined operation is executed. By way of example, in an operation for returning a movable portion such as a table to a reference point, the dog trips a deceleration limit switch in the vicinity of the reference point, whereupon an NC unit controlling the machine tool takes this as an indication that the table has reached the vicinity of the reference point and responds by providing a command for reducing the travelling velocity. Further, in a tool change operation, a tool rest is moved toward a tool change position. At the tool change position, a dog provided on the tool rest trips the limit switch, whereby the machine tool halts the tool rest at a stopping position and thereafter performs the tool change.
Thus, in the prior art, a dog and a limit switch are provided at appropriate locations and, when a prescribed limit switch is actuated, a predetermined operation is performed by the NC apparatus or the machine tool. This means that a dog and limit switch are essential, thereby increasing the number of component parts. Another disadvantage is that mounting and adjusting the dog and limit switch are troublesome operations.